153 lines
8.7 KiB
Markdown
153 lines
8.7 KiB
Markdown
---
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stage: none
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group: unassigned
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info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/product/ux/technical-writing/#assignments
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---
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# Flaky tests
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## What's a flaky test?
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It's a test that sometimes fails, but if you retry it enough times, it passes,
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eventually.
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## Quarantined tests
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When a test frequently fails in `main`,
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create [a ~"failure::flaky-test" issue](https://about.gitlab.com/handbook/engineering/workflow/#broken-master).
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If the test cannot be fixed in a timely fashion, there is an impact on the
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productivity of all the developers, so it should be quarantined by
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assigning the `:quarantine` metadata with the issue URL, and add the `~"quarantined test"` label to the issue.
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```ruby
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it 'succeeds', quarantine: 'https://gitlab.com/gitlab-org/gitlab/-/issues/12345' do
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expect(response).to have_gitlab_http_status(:ok)
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end
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```
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This means it is skipped unless run with `--tag quarantine`:
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```shell
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bin/rspec --tag quarantine
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```
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Once a test is in quarantine, there are 3 choices:
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- Fix the test (that is, get rid of its flakiness).
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- Move the test to a lower level of testing.
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- Remove the test entirely (for example, because there's already a
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lower-level test, or it's duplicating another same-level test, or it's testing
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too much etc.).
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## Automatic retries and flaky tests detection
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On our CI, we use [RSpec::Retry](https://github.com/NoRedInk/rspec-retry) to automatically retry a failing example a few
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times (see [`spec/spec_helper.rb`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/spec/spec_helper.rb) for the precise retries count).
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We also use a custom [`RspecFlaky::Listener`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/tooling/rspec_flaky/listener.rb).
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This listener runs in the `update-tests-metadata` job in `maintenance` scheduled pipelines
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on the `master` branch, and saves flaky examples to `rspec/flaky/report-suite.json`.
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The report file is then retrieved by the `retrieve-tests-metadata` job in all pipelines.
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This was originally implemented in: <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/13021>.
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If you want to enable retries locally, you can use the `RETRIES` environment variable.
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For instance `RETRIES=1 bin/rspec ...` would retry the failing examples once.
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To generate the reports locally, use the `FLAKY_RSPEC_GENERATE_REPORT` environment variable.
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For example, `FLAKY_RSPEC_GENERATE_REPORT=1 bin/rspec ...`.
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### Usage of the `rspec/flaky/report-suite.json` report
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The `rspec/flaky/report-suite.json` report is:
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- Used for [automatically skipping known flaky tests](../pipelines.md#automatic-skipping-of-flaky-tests).
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- [Imported into Snowflake](https://gitlab.com/gitlab-data/analytics/-/blob/master/extract/gitlab_flaky_tests/upload.py)
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once per day, for monitoring with the [internal dashboard](https://app.periscopedata.com/app/gitlab/888968/EP---Flaky-tests).
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## Problems we had in the past at GitLab
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- [`rspec-retry` is biting us when some API specs fail](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/29242): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/9825>
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- [Sporadic RSpec failures due to `PG::UniqueViolation`](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/28307#note_24958837): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/9846>
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- Follow-up: <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/10688>
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- [Capybara.reset_session! should be called before requests are blocked](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/33779): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/12224>
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- FFaker generates funky data that tests are not ready to handle (and tests should be predictable so that's bad!):
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- [Make `spec/mailers/notify_spec.rb` more robust](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/20121): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/10015>
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- [Transient failure in `spec/requests/api/commits_spec.rb`](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/27988#note_25342521): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/9944>
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- [Replace FFaker factory data with sequences](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/29643): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/10184>
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- [Transient failure in spec/finders/issues_finder_spec.rb](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/30211#note_26707685): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/10404>
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### Order-dependent flaky tests
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These flaky tests can fail depending on the order they run with other tests. For example:
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- <https://gitlab.com/gitlab-org/gitlab/-/issues/327668>
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To identify the tests that lead to such failure, we can use `scripts/rspec_bisect_flaky`,
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which would give us the minimal test combination to reproduce the failure:
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1. First obtain the list of specs that ran before the flaky test. You can search
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for the list under `Knapsack node specs:` in the CI job output log.
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1. Save the list of specs as a file, and run:
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```shell
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cat knapsack_specs.txt | xargs scripts/rspec_bisect_flaky
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```
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If there is an order-dependency issue, the script above will print the minimal
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reproduction.
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### Time-sensitive flaky tests
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- <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/10046>
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- <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/10306>
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### Array order expectation
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- <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/10148>
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### Feature tests
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- [Be sure to create all the data the test need before starting exercise](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/32622#note_31128195): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/12059>
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- [Bis](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/34609#note_34048715): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/12604>
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- [Bis](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/34698#note_34276286): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/12664>
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- [Assert against the underlying database state instead of against a page's content](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/31437): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/10934>
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- In JS tests, shifting elements can cause Capybara to mis-click when the element moves at the exact time Capybara sends the click
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- [Dropdowns rendering upward or downward due to window size and scroll position](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/17660)
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- [Lazy loaded images can cause Capybara to mis-click](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/18713)
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- [Triggering JS events before the event handlers are set up](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/18742)
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- [Wait for the image to be lazy-loaded when asserting on a Markdown image's `src` attribute](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/25408)
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- [Avoid asserting against flash notice banners](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/79432)
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#### Capybara viewport size related issues
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- [Transient failure of spec/features/issues/filtered_search/filter_issues_spec.rb](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/29241#note_26743936): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/10411>
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#### Capybara JS driver related issues
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- [Don't wait for AJAX when no AJAX request is fired](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/30461): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/10454>
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- [Bis](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/34647): <https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/12626>
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#### Capybara expectation times out
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- [Test imports a project (via Sidekiq) that is growing over time, leading to timeouts when the import takes longer than 60 seconds](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/22599)
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### Hanging specs
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If a spec hangs, it might be caused by a [bug in Rails](https://github.com/rails/rails/issues/45994):
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- <https://gitlab.com/gitlab-org/gitlab/-/merge_requests/81112>
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- <https://gitlab.com/gitlab-org/gitlab/-/issues/337039>
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## Resources
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- [Flaky Tests: Are You Sure You Want to Rerun Them?](https://semaphoreci.com/blog/2017/04/20/flaky-tests.html)
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- [How to Deal With and Eliminate Flaky Tests](https://semaphoreci.com/community/tutorials/how-to-deal-with-and-eliminate-flaky-tests)
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- [Tips on Treating Flakiness in your Rails Test Suite](https://semaphoreci.com/blog/2017/08/03/tips-on-treating-flakiness-in-your-test-suite.html)
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- ['Flaky' tests: a short story](https://www.ombulabs.com/blog/rspec/continuous-integration/how-to-track-down-a-flaky-test.html)
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- [Using Insights to Discover Flaky, Slow, and Failed Tests](https://circleci.com/blog/using-insights-to-discover-flaky-slow-and-failed-tests/)
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---
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[Return to Testing documentation](index.md)
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